Comment by Animats

I only wrote one graphics application in Mesa, as a student at Stanford. I never used Cedar or SafeMesa or any of the Alto successors, although I visited PARC a few times and saw them used.

Xerox had to invent Mesa because they were previously stuck writing BCPL, a predecessor to C sometimes known as the British Cruddy Programming Language.

Xerox's world model was closed systems with a few beautiful applications written by experts. End users were not to be allowed access to the guts of the software. The realization of this was the Xerox Star, which was a nice, and very expensive, world processor with a few additional applications. (Visualize a system that runs Microsoft Office and nothing else.) The idea that ordinary people would write application programs was completely alien to Xerox. Their market was secretaries.